A reactor is one type of component of a circuit for increasing or reducing voltage. JP 2011-119664A discloses a reactor including a coil in which a pair of winding portions (a coil element) obtained by helically winding a winding wire are arranged side by side, and an annular magnetic core formed by combining a plurality of core pieces, as a reactor used for a converter installed in a vehicle such as a hybrid automobile.
The magnetic core disclosed in JP 2011-119664A includes middle core pieces disposed inside the winding portions, end core pieces that are not covered by the winding portions and in which a coil is not disposed, and gap members that are interposed between adjacent core pieces. A surface of the end core piece that is opposite to an installation target when the reactor is attached to the installation target protrudes further toward the installation target than a surface of the middle core piece that is opposite to the installation target, and serves as an installation surface. As a result of a decrease in the thickness in the axial direction of the winding portions caused by this protrusion, the end core piece can reduce the installation surface. Also, all of the middle core pieces and the end core pieces are powder compacts, and these core pieces are independent members, making the core pieces into a simple three dimensional shape such as a cuboidal shape.
A reactor is desirable that has a small installation area, low loss, and excellent productivity.
As described above, the length in the axial direction of the winding portions in the reactor decreases due to the shape in which the end core pieces further protrude than the middle core pieces, resulting in the reactor having a small installation area. However, since the end core pieces and the middle core pieces are independent from each other, the number of assembling components will increase, the number of steps will increase, and the productivity of reactors will decrease. Because a surface of the end core piece that joins the middle core piece is a uniform flat surface, a difficulty in positioning of these core pieces will also reduce the productivity.
Also, if gaps are provided between the end core pieces and the middle core pieces, magnetic flux leaks from gap portions to protruding portions of the end core pieces. If this magnetic flux leak intersects the coil, loss such as copper loss may increase. In the reactor of JP 2011-119664A, in order to reduce this loss, a relative magnetic permeability of the gap members is greater than 1 and less than 1.5. However, the number of steps of manufacturing these specific gap members will increase, and the productivity of reactors will decrease.
The present invention has been made in view of the above-described circumstances, and it is an object thereof to provide a reactor that has a small installation area, low loss, and excellent productivity.